1. Field of the Invention
The present invention generally relates to a method of manufacturing an organic EL (electroluminescent) display using a sealing glass substrate, and more specifically to a method of manufacturing an organic EL display using a sealing glass substrate provided with an escape groove for adhesive adjacent to an adhesion region.
2. Description of the Related Art
A conventional sealed organic EL display, in the type called a bottom emission type in particular, has a structure as shown in FIGS. 1A-1C. The organic EL display in the sectional view of FIG. 1A comprises a laminate 12 including a transparent electrode, an organic EL layer, a reflection electrode formed on a glass substrate 11, and a lead out terminal 17a connecting electrically to the reflection electrode of the laminate 12. An adhesive 13 is applied around the laminate 12 and adheres the laminate to a sealing glass substrate 14. The organic EL layer, being very vulnerable to oxygen and moisture, easily loses light emission ability upon exposure to the atmosphere. Accordingly, an organic EL layer is usually sealed by a sealing glass substrate 14 having a moisture absorber 15 disposed opposing the laminate 12 in a chamber with extremely reduced oxygen and moisture. To prevent the organic EL layer and other laminated films from being touched, and to ensure that a space is provided for accommodating the moisture absorber, a recess may be created in the sealing substrate in the portion opposing the laminate of the organic EL layer and other films. The adhesive 13 can be formed from an ultraviolet light-hardening type adhesive, for example. FIG. 1B is a plan view of this structure taken from the side of the glass substrate 11. An organic EL display area for light emission from the organic EL layer is formed in the location corresponding to the laminate 12. A sealing region is formed in the area corresponding to the adhesive 13. FIG. 1C is a plan view of this structure taken from the side of the sealing glass substrate 14, in which lead out terminals 17a and 17b are exposed. The lead out terminal 17a electrically connects to the reflection electrode and the lead out terminal 17b electrically connects to the transparent electrode.
Mass production of organic EL displays is generally carried out by forming multiple organic EL display areas on a glass substrate, sealing with a sealing glass substrate, and then cutting those substrates to form multiple organic EL displays. FIG. 2 shows a sealing substrate 21 and a substrate 25 for multiple organic EL displays. The substrate 25 for multiple organic EL displays comprises multiple combinations of a laminate 26 containing a transparent electrode, an organic EL layer, and other layers (which forms an organic EL display area together with a reflection electrode) and a lead out terminal 27 electrically connecting to the reflection electrode in contact with the laminate 26. The sealing substrate 21 has recesses 22 at positions opposing the respective laminates 26. Adhesive is applied around each recess 22 by means of a dispenser or by screen printing and the two substrates are laminated as shown in FIG. 3A-3C. FIG. 3A is a sectional view; FIG. 3B is a plan view taken from the side of the substrate 25 for multiple organic EL displays; and FIG. 3C is a plan view taken from the side of the sealing substrate 21. In the laminating process, the adhesive (ultraviolet light-hardening resin) is pressed by exerting external pressure after the elements are combined, or the elements are combined under a reduced pressure and then the atmospheric pressure is restored. After curing the adhesive by irradiating it with ultraviolet light, the sealing substrate 21 is cut along the lines 32 and the substrate 25 for multiple organic EL displays is cut along the lines 31, to obtain the shape shown in FIG. 1A-1C. The cutting is carried out primarily by means of a scribe method, in which small nicks are formed on the glass surface using a diamond cutter or the like, and then developing the cracks by striking from the back side or exerting a stress, to cleave the glass.
The use of a material other than glass for the sealing substrate has been proposed in Japanese Unexamined Patent Application Publications.2001-189191 and 2000-100562. In the structure of 2001-189191, two grooves are formed at both sides of an adhesion application region of a sealing plate of stainless steel manufactured by drawing control, and expansion of the adhesive is restrained. The sealing plate in this arrangement is, however, not planar and has a shape that is difficult to fabricate in glass. In addition, the adhesive is permitted to expand laterally beyond the grooves and the structure does not take into account the cutting after sealing. Japanese Unexamined Patent Application Publication 2000 -100562 discloses a structure that restrains invasion of adhesive into a space for accommodating a light emitting part by disposing a groove on an adhesive application region in a sealing body of metal or the like. The sealing board of this structure is again not planar and difficult to fabricate in glass. The structure restrains invasion of adhesive into a space for accommodating a light emitting part by permitting outward expansion of the adhesive, thus, does not consider cutting work after the sealing.
In the method of manufacturing an organic EL display as shown in FIGS. 1A-1C from the combination of FIGS. 3A-3C, the adhesive may run off from the predetermined location and extend laterally in the process of laminating the two substrates 21 and 25. If the run off adhesive expands to the cutting position, the nick produced fails to cut the glass at the desired position. (See FIG. 6A.) Even if a nick is produced in an area the adhesive exists, the crack does not extend or extends to a direction where the adhesive is absent, generating defects such as cracking, burrs, and flaking. Accordingly, a means is taken in which the cutting position is determined in the outside region from the extended adhesive with enough clearance. Or if some restriction is imposed on the cutting position, the adhesion width is narrowed or the adhesive is not pressed strongly, preventing the adhesive from expanding uncontrollably from the position at which the adhesive is applied.
Control of the expanded width of the adhesive becomes difficult as the degree of squeezing of the adhesive increases and needs excessive space. As a result, a peripheral region of an EL display area called “a picture frame” expands and the external dimension of the display enlarges, decreasing the number of displays that can be produced from one substrate and causing an increase in the cost. The narrowing of adhesion width and the decrease in the amount of squeezing, on the other hand, deteriorate sealing performance and readily cause degradation of the organic EL layer due to oxygen or moisture.
Since the end milling work for forming the recess on the glass substrate generates distortion of several tens of microns in height around the recess, it is difficult to apply adhesive uniformly around the recess. If the application is non-uniform, then uniform pressing still causes different degrees of expansion of the adhesive (adhesion width) from place to place. If a precise application of adhesive is desired on a distorted surface, a costly system would be needed that measures the height of the surface to which the adhesive is to be applied and conducts application of the adhesive strictly following the height.